Acute severe asthma

Acute severe asthma is severe bronchospasm in a patient with a history of asthma.

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What causes acute severe asthma?

• History of asthma with previous emergency hospitalizations.
• Respiratory tract infections.
• Trigger factors such as stress, cold, exercise, smoking, allergen.
• Premature or low birth weight babies.

What are the symptoms of acute severe asthma?

Acute severe asthma is clinically expressed by the following symptoms:

• Peak expiratory flow rate (PEFR) < 33-50% of best or predicted, SpO2 < 92%, HR 120 bpm (<5 years) or > 130 bpm (2-5 years), RR > 30 bpm (>5 years) or > 50 bpm (2-5 years), involvement of accessory muscles in the act of breathing.

Life-threatening asthma: Any of the following in a patient with acute severe asthma:

• PEFR < 33% of best or predicted, SpO2 < 92% or PaO2 < 8 kPa (60 mmHg), normal PaCO2 (4.6-6 kPa, 35-45 mmHg), hypotension, fatigue, confusion or coma, silent lung fields, cyanosis, decreased respiratory effort.

Near fatal asthma:

• increased PaCO2 and/or need for mechanical ventilation
• Confusion or drowsiness, maximum involvement of accessory muscles in the act of respiration, exhaustion, SpO2 < 92% in air, HR 140 bpm, inability to speak.

How is acute severe asthma recognized?

• SpO2, PEFR or FEV1 (>5 years).
• If the condition is critical: blood gases, chest x-ray, plasma theophylline level.

Differential diagnosis

Wheezing in the lungs can be of other origins:

• bronchiolitis or croup; o aspiration of a foreign body - asymmetry on auscultation;
• epiglottitis - very rare after the introduction of the vaccine against Haemophilus influenza B;
• pneumonia - can be both the primary cause of wheezing and a trigger for an asthma attack;
• tracheomapia.

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Immediate action

Acute severe asthma:

• salbutamol 10 inhalations through a dispenser and adapter ± face mask or salbutamol inhaler (2.5-5 mg);
• prednisolone orally 20 mg (2-5 years), 30-40 mg (>5 years) or hydrocortisone intravenously 4 mg/kg;
• salbutamol repeat every 30 min, add ipratropium bromide 250 mcg by inhaler every 20-30 min.

Life-threatening asthma:

• immediately salbutamol inhaler 2.5-5 mg;
• ipratropium bromide inhaler 250 mcg;
• hydrocortisone intravenously 4 mg/kg;
• bronchodilators every 20-30 minutes;
• adrenaline subcutaneously 10 mcg/kg (solution 0.01 ml/kg 1:1000; or 0.1 ml/kg 1:10,000).

Further management

• If there is improvement, monitor SpO2, inhale prednisolone orally every 3-4 hours for 3 days, transfer to a specialized department.
• If, despite the treatment, the condition worsens:
  • intravenous salbutamol, titrating according to effect, up to 15 mcg/kg over 10 min, then infusion of 1-5 mcg/kg/min;
  • aminophylline: loading dose 5 mg/kg, then intravenous infusion 1 mg/kg/h;
  • continue inhaling every 20 minutes;
  • consider using adrenaline (0.02-0.1 mcg/kg/min);
  • magnesium sulfate intravenously 40 mg/kg (maximum 2 g).
• If respiratory failure worsens: intubate, ventilate and transfer to pediatric ICU.

Special considerations

• In severe asthma with very high airway pressures, decreased tidal volumes and capnographic curve jumps, mechanical ventilation may be difficult.
• Manual ventilation with a low-compliance system may be required, but monitoring of airway pressures, especially inspiratory pressures, will be essential. Airway pressures of up to 30-40 cm H20 may be required. Elevated pressures indicate the need for maximal use of bronchodilators.
• All inhalational anesthetics cause bronchial relaxation and may be useful in severe attacks. Care must be taken to remove the used gas mixture.
• These children are usually dehydrated, so induction of anaesthesia for intubation should be preceded by a 20 ml/kg crystalloid infusion. Slow administration is preferred, but rapid sequence induction may be required in nonfasted patients. Propofol and ketamine are ideal.
• Peak expiratory flow rate in children: This is a simple method of measuring airway obstruction, allowing to determine the moderate to severe degree of the disease. The measurement is made using a standard Wright peak flow meter.